GB1575541A - Process for the production of carboxylic acid esters by catalytic oxidation of alcohols - Google Patents

Description

PATENT SPECIFICATION ( 11) 1 575 541

-Z ( 21) Application No 15720/77 ( 22) Filed 15 Apr 1977 ( 19) v) ( 31) Convention Application No 2616979 ( 32) Filed 17 Apr 1976 in X U) ( 33) Fed Rep of Germany (DE)

3 b ( 44) Complete Specification Published 24 Sep 1980

U) ( 51) INT CL 3 CO 7 C 69/04 69/14 69/24 ( 52) Index at Acceptance C 2 C 20 Y 30 Y 366 368 37 X 409 491 628 \ CE FB ( 54) A PROCESS FOR THE PRODUCTION OF CARBOXYLIC ACID ESTERS BY CATALYTIC OXIDATION OF ALCOHOLS ( 71) We, CHEMISCHE WERKE HULS AKTIENGESELLSCHAFT, a German Company, of 4370 Marl, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement:-

It is already known (US-PS 3,257,448) that carboxylic acid esters can be prepared by 5 oxidizing a mixture of an alcohol and an aldehyde in liquid phase A mixture of palladium chloride and copper chloride serves as the catalyst in that process In addition the presence of a large amount of a lithium salt is necessary to bind the water formed Such a catalyst system is decidedly complicated and difficult to deal with.

Moreover a process is disclosed in US-PS 3,639,449 in which an alcohol or a mixture of an 10 alcohol and an aldehyde is oxidised to an ester in the liquid phase or in the gas phase at elevated temperature with molecular oxygen in the presence of a precious metal catalyst In a reaction in the liquid phase activated carbon or diatomaceous earth is used as carrier material Precious metal catalysts are expensive and moreover the catalysts undergo loss of metal by mechanical attrition during operation and with the high cost of precious metals this 15 is adverse economically Furthermore it has been found that in the liquid phase aldehydes (particularly formaldehyde) owing to their strong affinity inactivate the catalyst and this is confirmed in a later publication of the inventor of US-PS 3,639,449 cited in C A, 79, 4594 a ( 1973) Aldehydes are however always formed in the oxidation of alcohols so that such a catalyst is hardly useful for a long period 20 The present invention seeks to develop a process in which a catalyst system is used which is economical, has good effectiveness and cannot lead to disturbances by reason of catalyst attrition.

According to the invention there is provided a process for the production of a carboxylic acid ester by catalytic oxidation of an alcohol in the liquid phase, wherein a primary alcohol 25 of 1 to 4 carbon atoms or a mixture of a primary alcohol and an aldehyde both of 1 to 4 carbon atoms is oxidised at a temperature of from 100 to 250 'C with molecular oxygen in the presence of a catalytic amount of a compound of cobalt, manganese, chromium or iron and a catalytic amount of an acid of a 1st dissociation constant K, of more than 10-3, both dissolved in the reaction mixture 30 The reaction proceeds according to the equation:R-CH 20 H + 02 R-COOCH 2-R + 2 H 20 (R being hydrogen or a radical of up to 3 carbon atoms) Methanol, ethanol, n-propanol 35 and n-butanol are examples of alcohols which may be used Methyl formate is formed from methanol, ethyl acetate from ethanol, and so on When a mixture of alcohols is used a mixture of the corresponding esters is obtained Thus the esters: methyl formate, methyl acetate, ethyl formate and ethyl acetate are formed from a mixture of methanol and ethanol The ratio of the esters formed fluctuates according to the reaction conditions 40 It is also possible to use a mixture of an alcohol and an aldehyde, both of 1 to 4 carbon atoms.

A combination of a metal compound and an acid both selected from certain classes is used as the catalyst and the components are homogeneously dissolved in the reaction system The metal compound may be any of the compounds of manganese, cobalt, 45 2 1575 5412 chromium and iron provided they are sufficiently soluble to dissolve in the reaction system in the amount used and provided constituents contained in addition to the metal in the metal compound, e g anions, cations or complex ligands, do not cause the reaction to cease by intercepting radicals or other damaging attack in the catalyst system Accordingly, metal compounds which may be used include salts in which the metal is present either in the anion 5 or as the cation, metal complexes and other metal compounds, for example oxides.

Acetates, naphthenates or acetylacetone complexes are particularly suitable for use but good results are also achieved with sulphates, nitrates, chlorides, oxides and chromates.

Mixtures of two or more metal compounds may also be used as catalysts.

All acids whose 1st dissociation constant is more than 10-3, for example H Cl, HNO 3, 10 H C 104, H 2504, H Br, H 3 P 04; and HI amongst inorganic acids, and organic acids such as methanesulphonic acid p-chlorobenzoic acid, oxalic acid and trichloroacetic acid, are suitable as acids provided that they or their oxidation or hydrolysis products formed in the reaction mixture do not bring the reaction to a standstill by trapping radicals or by other damaging attack in the reaction The acids may also be produced in situ from compounds 15 which are hydrolysed with the water present in the reaction mixture For example BF 3 may be added to the reaction mixture so that the HF or HBF 4 formed acts as a catalyst For economic reasons those acids are always used which attack the reactor material least.

Phosphoric acid and sulphuric acid are particularly suitable but good results are achieved also with oxalic acid and trichloroacetic acid Mixtures of acids may also be used 20 The metal compounds have catalytic effectiveness even in extremely small amounts The concentration generally used is from 0 2 to 100 ppm (calculated as metal) based on the weight of alcohol used At a metal concentration less than 0 2 ppm the catalytic action falls off and above a concentration of 100 ppm no additional effect can be noticed The range of concentration from 1 to 10 ppm is the most viable range industrially Sometimes the 25 concentration of metal salts in the reactor which is attributable to corrosion of the reactor material (even in the case of refined steel vessels) is high enough to cause catalytic activity.

The acid concentration in the reaction mixture is desirably at least 5 ppm based on the amount by weight of the alcohol used because below this concentration the catalytic effectiveness falls off If an acid concentration of 100 ppm is exceeded a deterioration in the 30 catalytic action is sometimes noticeable Phosphoric acid may be used in much higher amounts than 100 ppm but increasing the concentration of phosphoric acid beyond 100 ppm does not give better results A range of concentration from 50 to 100 ppm is generally used industrially.

The separation of the catalyst from the reaction product in so far as it is necessary at all 35 at the lower concentrations may be carried out by precipitation and filtration or particularly advantageously by ion exchange.

Molecular oxygen, suitably in the form of pure oxygen, air or a mixture of oxygen and nitrogen, is used as the oxidizing agent Naturally the oxygen may be used mixed with other gases inert under the reaction conditions The use of air is particularly simple and 40 economical.

The reaction is carried out at a temperature of from 1000 to 250 'C The speed of reaction is only very low at below 100 'C and the complete oxidation of the alcohols into CO 2, CO and H 20 increases markedly above 250 'C The range of temperature from 1000 to 200 'C is preferred because in this range a high speed of reaction prevails with a fairly low production 45 of byproducts Since the reaction takes place in the liquid phase a pressure which is equal to or higher than the vapour pressure of the alcohol used at the reaction temperature has to be used to maintain the liquid phase.

The oxidative esterification of the alcohols may be carried out batchwise or continuously.

The continuous method is generally used industrially Reactors usually employed for 50 gas-liquid reactions, for example bubble column reactors, may be used as the reactors.

The reaction period for the oxidative esterification is usually from ninety minutes to fifteen hours The longer the oxidation period is, the better is the alcohol conversion Of course the amount of cleavage products such as CO 2, CO, CH 4 and H 20 increases with longer oxidation periods When the liquid and gaseous phases are mixed particularly 55 intimately the reaction period may also be shortened considerably It has been found that occasionally a certain time (induction period) elapses before reaction commences Since the induction period is extremely short when phosphoric acid is used as the acid component it is recommended in such cases to start the reaction by using phosphoric acid or to supply a small amount of phosphoric acid initially to the reaction mixture 60 Aldehyde, acetal and carboxylic acid are formed as byproducts in the oxidative esterification These byproducts (after the separation of the ester formed, conveniently by distillation) maybe added to the reaction mixture or, in the case of batchwise operation, to a new reaction batch (provided they are not used in some other way) so that in the final products only water and small amounts of CO, CO 2 and CH 4 are present beside the desired 65 1,575 541 3 1 575 541 3 ester.

When the ester formed in the reaction has a lower boiling point than the starting alcohol it is advantageous to distil of the ester formed continuously from the reaction mixture.

Hydrolysis of the ester formed by the water of reaction can be kept slight in this way The formation of strongly corrosive formic acid may be suppressed strongly particularly in the 5 production of methyl formate in this way.

The catalyst according to this invention has the advantage of a good selectivity at short reaction periods and a strongly decreased proportion of the total oxidation to CO and CO 2.

The components of the catalyst are decidedly economical and moreover are used in extremely low concentrations Inhibition of the action of the catalyst by reaction products 10 does not take place Even when the water content of the reaction mixture is more than 10 % by weight the reaction proceeds at satisfactory speed so that even in this case a high conversion is achievable without any decrease in selectivity so that economical performance of process is possible.

15 Examples 1 to 17 and 21 to 27 Methanol or ethanol is oxidised in a reactor provided with a reflux condenser The reactor is made from an alloy of nickel, chromium and molybdenum (HASTELLOY C HASTELLOY is a Registered Trade Mark) and is provided internally with a coating of gold galvanically to avoid corrosion In each case 230 g of alcohol and also metal compound 20 and acid are placed in the reactor The reactor is heated to the reaction temperature and then air is passed in as the oxidising agent After the reaction has started, fresh methanol with catalyst dissolved in it is continuously supplied and the corresponding amount of reaction product is withdrawn The rate of feed is chosen so that a specific mean residence time for the methanol in the reactor results In batchwise operation fresh methanol is not 25 added but the operation is stopped after a certain reaction period The concentration of catalyst is monitored by analyses The liquid reaction product withdrawn from the reactor and also the escaping offgas are analysed The results obtained when various paramaters are varied are collected in the Table.

30 Examples 18 to 20 Catalytic amounts of metal compound and acid are added to 150 g of nbutanol in a glass bubble column reactor provided with a reflux condenser and means for entraining out the water (water separator) After the reaction temperature has been reached air is passed in as the oxidising agent The results are collected in the Table 35 1 575 541 Example Alcohol 1 CHOH 2 CHOH 3 CHOH 4 CHOH CHOH 6 CHOH 7 CHOH 8 CHOH 9 CHOH CHOH 11 CHOH 12 C 2 HOH 13 C 2 HOH 14 C^HOH C 2 I-1 OH 16 C 2 HOH 17 C 2 HOH 18 C 4 HOH 19 C^HOH C 4 HOH TABLE

Temp Press Amount Catalyst ('C) (bar) of air Metal compound (NI/h) (ppm, Metal) 109 109 108 18 70 2,5 Co 11-acetate 18 70 100 Mn 11-acetate 23 70 3 Cr Ill-acetylacetonate 18 70 3,5 Fe Ill-acetylacetonate 18 70 50 Co II + 2,5 Mn III-acetate 23 70 2 Co I 1-acetate 23 70 18 70 18 70 18 70 105 14 40 14 40 6,6 50 6,6 75 40 14 40 1 15 1 15 1 15 4 Co Il-acetate 2 Co 11-acetate 2 Co 11-acetate Co II-naphthenate 3,5 Fe III + 3,5 Co IIIacetylacetonate Co Ill-acetylacetonate Co Il-acetate 8 Co II-" Co II-" CO II-, Co-III-acetylacetonate Cr III-acetylacetonate Co III-acetylacetonate Acid (ppm) Residence time Reaction period (h) HP 04 3,5 680 HPO, 5 (disk) H 2504 3,5 H 3 P 04 3,6 680 H 3 P 04 4,3 Oxalic 2,3 acid CCI 3 COOH 3,1 H 3 i P 041,9 H 3 P 04 2,0 680 H 3 P 04 3,5 (disk) H 13 P 042,6 11000 H 3 P 04 HP 04 4500 HP 04 H 504 11000 HPO, 600 HP 04 700 HPO, 1200 HP 04 disk} 6 (") (") () Conversion (wt %) 28,7 40,0 44,8 45,3 35,2 35,2 33,8 21,1 231,11) 43,6 60,2 0 0 58 14 23 Ausbeute, bezogen auf Umsatz (%) Ester Acetal Aldehyd Acid 57,5 50,9 51,0 58,0 55,9 51,7 58,6 47,6 92,2 53,5 70,8 37,8 34,9 42,3 38,6 42,2 45,1 35,4 47,4 43,1 25,7 1,8 1,1 1,9 0,7 1,3 1,9 1,7 2,8 3,9 1,4 -0,6 1,5 1,4 1,4 1,5 1,7 3,1 0,7 2,0 0,1 1,5 1,4 1,4 0,9 3,4 0 2,2 0 3,9 0,4 1,6 0,9 2,0 + CH 4 CO + C 02 22 21 15 11 34 24 22 11 9 32 2 12 45 9 10 10 17 7 82 9 4 3 2 24 21 36 5 3 59 1 1 16 8 ( 1) CH 30 H conversion ( 2) CH 30 H contains 20 %H 20 ( 3) CH 30 H contains 20 %of acetal ( 4 Coprtv te.

4 h.

( 2) ( 3) ( 4) ( 4) -1 j U 1, ( 4) Comparative test.

Example Alcohol Temp Press Amount Catalyst (C (ba) of air Metal compound (C) (bar) (NI/h) (ppm, Metal) Acid (ppm) J 4 Residence time Reaction period (h) Conversion (wt %) Yield based on conversion (%) Ester Acetal Aldehyde Acid CO 2 + CO + CIH 4 21 CH 3 OH 145 18 70 3 Cr VI-oxide l UU r 13 rt 22 CH 3 OH 160 23 43 3 Na 2 Cr 2 07 100 H 3 P( 23 CH 3 OH 160 23 43 4 Fe III-chloride 100 H 3 P( 23 3 O H O H 3 P 04 24 CH 3 OH 150 18 70 2 Co Il-acetate 6 H 3 P 4 CH 3 OH 160 23 70 0,4 Co III-acetylacetonate76 H 3 PO 0,1 Fe III0,2 Cr III " 26 CH 3 OH 160 23 70 2 Co Il-acetate 100 H 3 P( 1 Cr III-acetylacetonate 27 CH 3 OH 160 23 70 3 Cr l II-acetylacetonate 100 BF 3 4 2,6 36,5 2,8 48,1 2,3 29,3 3,5 24,3 2,5 31,6 ( 1) 04 2,4 47,7 66,1 47,9 41,4 92,0 46,6 28,5 44,6 55,8 33,2 (o) 48,9 44,1 3,4 1,2 1,1 0,9 1,7 2,8 1,4 1,7 4,4 2,3 0,4 1,6 2,2 2,8 3,0 ( 5) 2,1 2,3 2,6 ( 6) 2,2 48,2 57,6 34,0 1,4 3,7 3,3 ( 5) 12 5 % by weight of acetal in CH 3 OH ( 6) 13 % by weight of formaldehyde + CH 3 OH used.

lI-Pl C/6 1 575 541 6

Claims (1)

1. WHAT WE CLAIM IS:-

   1 A process for the production of a carboxylic acid ester by catalytic oxidation of an alcohol in the liquid phase, wherein a primary alcohol of 1 to 4 carbon atoms or a mixture of an aldehyde and a primary alcohol both of 1 to 4 carbon atoms is oxidised at a temperature of from 100 to 250 C with molecular oxygen in the presence of a catalytic amount of a 5 compound of cobalt, manganese, chromium or iron dissolved in the reaction mixture and in the presence of a catalytic amount of an acid having a 1st dissociation constant K, which is greater than 10-3 also dissolved in the reaction mixture.

   2 A process as claimed in claim 1 wherein the compound of cobalt, manganese, chromium or iron is used in an amount of from 0 2 to 100 ppm, reckoned as metal, based on 10 the weight of alcohol used.

   3 A process as claimed in claim 1 wherein the compound of cobalt, manganese, chromium or iron is used in an amount of from 1 to 10 ppm, reckoned as metal, based on the weight of alcohol used.

   4 A process as claimed in any of claims 1 to 3 wherein the acid is used in an amount of 5 15 to 100 ppm based on the weight of alcohol used.

   A process as claimed in any of claims 1 to 3 wherein the acid is used in an amount of to 100 ppm based on the weight of alcohol used.

   6 A process as claimed in any of claims 1 to 5 wherein the oxidation is carried out at a temperature of from 1000 to 200 'C 20 7 A process as claimed in any of claims 1 to 6 wherein an acetate or naphthenate is used as the compound of cobalt, manganese, chromium or iron.

   8 A process as claimed in any of claims 1 to 7 wherein phosphoric acid or sulphuric acid is used as the acid.

   9 A process as claimed in any of claims 1 to 8 wherein the acid is produced in situ by 25 hydrolysis of a compound present in the reaction mixture with water which is also present.

   A process as claimed in any of claims 1 to 9 wherein air is used for the oxidation.

   11 A process as claimed in any of claims 1 to 10 wherein the oxidation is carried out continuously.

   12 A process as claimed in any of claims 1 to 11 wherein the reaction period is from 30 ninety minutes to fifteen hours.

   13 A process as claimed in any of claims 1 to 12 wherein the liquid phase and the gas phase are mixed intimately.

   14 A process as claimed in any of claims 1 to 13 wherein the reaction is started by means of phosphoric acid 35 A process as claimed in any of claims 1 to 14 wherein the ester formed is distilled off continuously from the reaction mixture when it has a lower boiling point than the starting alcohol.

   16 A process for the production of a carboxylic acid ester carried out substantially as described in any of the foregoing Examples 1 to 11 or 14 to 27 40 17 A carboxylic acid ester when obtained by a process as claimed in any of claims 1 to 16.

   J Y & G W JOHNSON, Furnival House, 45 14-18 High Holborn, London WC 1 V 6 DE, Chartered Patent Agents, Agents for the Applicants.

   Printed for Her Majesty's Stationery Office by Croydon Printing Company Limited Croydon, Surrey, 1980.

   Published by The Patent Office 25 Sonthampton Buildings, London, WC 2 A LA Yfrom which copies may be obtained.

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